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Abstract: The present paper deals with CFD study of flow and thermal characteristics in air-conditioned rooms under turbulent mixed convection conditions. Air enters room from a sidewall slot flush with isothermal ceiling and leaves through a slot in opposite wall flush with floor. Velocity and temperature distributions are determined by a CFD model that has been previously validated by comparison with experimental data. Rigorous dimensional analysis shows that performance of the air-distribution system depends on: supply Reynolds number Re d , Grashof number Gr d (or Archimedes number Ar d ), room aspect ratio L/H, dimensionless heights of supply and return ports (d/H and t/H), where H is room height. For a room with fixed geometry, the effects of Re d and Gr d (or Ar d ) are investigated systematically by varying one parameter at a time. Results show that ceiling average Nusselt number (Nu d,av) increases with Re d and decreases with Gr d (or Ar d ). For a given Gr d , the heat removal index (HRI) increases with Re d up to Re d  ≈ 9000, then stays practically constant thereafter. For a given Re d , HRI decreases with increasing Gr d (or Ar d ). A criterion for distinction between forced and mixed convection situations is developed, resulting in a critical Archimedes number of 0.11. Results further indicate that Ar d alone, irrespective of the particular values of Re d and Gr d , determines to a reasonable extent Nu d,av and HRI when Ar d is above its critical value. Streamlines and temperature contours are found to be consistent with other results and helped explain them. [Copyright &y& Elsevier]

Abstract: The wave-finned flat tube heat exchangers are widely used in air-cooled condensers of a power plant. Due to the oblique arrangement of the wavy fins on the A-frame tube bundles of the air-cooled condenser, the finned tube is prone to fouling thus the thermo-flow performances of air-cooled condensers are likely to become deteriorated. A new configuration of wave-finned flat tube, in which the fin surface rotates to be perpendicular, is proposed in this paper to prevent the fouling from gathering on the finned tube. The physical and mathematical models for the fluid and heat flows of the cooling air through the present and proposed wave-finned flat tube bundles are setup, and the thermo-flow characteristics are compared. For the proposed finned tube, the influences of the fin pitch, height and the Reynolds number on the flow and heat transfer performances are investigated, and the correlations of the friction factor and Nusselt number are recommended. The results show that the buoyancy effect should be taken into account for the correlation of the friction factor at low Reynolds numbers, but this buoyancy force can be ignored for the Nusselt number. [Copyright &y& Elsevier]